The overall objective of this project will be to investigate mechanisms whereby T lymphocytes regulate the development of cell-mediated immune responses to alloantigens. The work will be focused primarily on the function of alloantigen-activated murine suppressor T cells in the control of mixed leukocyte reactions and the generation of cytotoxic T lymphocytes. Soluble products of such suppressor cells will be isolated and characterized with particular attention to differences between factors which control of proliferative and cytotoxic responses. The role of gene product of the mouse major histocompatibility complex (H-2) in regulatory interactions between T cell subpopulations will also be explored in detail. As feasible experimental models developed in mice will be extended to in vitro studies of the regulation of human cell-mediated immune responses.